In-situ monitoring of atmospheric pressure tin oxide CVD using coherent anti-Stokes Raman scattering

Coherent anti-Stokes Raman scattering (CARS) has been used to investigate the mechanisms involved in the atmospheric pressure chemical vapour deposition (CVD) of tin oxide films on glass using dimethyltindichloride (DMT) and oxygen and/or water at 645°C. A novel compact CARS experimental system which operates using a collinear sampling geometry was designed and constructed around a conventional Nd:YAG/dye laser combination. This system facilitates the sampling of gas phase species at specific points within the reactor. This high spatial resolution has been used to investigate the variation in concentration of a major reaction product, methane as a function of position within the reactor. In addition, we report on the likelihood of detection of methyl radicals, which are believed to form via the decomposition of DMT, under growth conditions and the use of CARS in probing the gas-phase temperature within the reactor in an entirely non-invasive manner via analysis of the vibration-rotation structure of the CARS spectra associated with the N₂ process gas.